The invention relates to photopolymerizable compositions of matter for application to human nails to provide formed-in-place artificial nails.
Polymerizable compositions of matter for various dental and medical uses are known in the prior art. See generally U.S. Pats. Nos. 3,066,112; 3,179,623; 3,539,533; and 3,751,399. The prior art also suggests the use of photopolymerizable compositions for use in restorative dentistry. See e.g., U.S. Pat. No. 3,709,866.
Polymerizable compositions formulated for use in dentistry must satisfy a combination of rigorus criteria imposed by the conditions which exist in the mouth and to which such compositions are subjected in the course of mastication. Polymerizable dental restorative compositions must strongly adhere to tooth enamel, the hardest substance in the body. Such products must cure or set rapidly with only moderate exotherm. The cured product must be long lasting and hence characterized by high compressive strength, high modulus of elasticity in compression, flexure and tension, excellent wear resistance, excellent resistance to the effects of water, including hydrolysis. In general, these essential properties of polymerizable compositions for dental application are afforded by the selection of monomers to provide a low oxygen to carbon ratio and a high cross-link density and by the use, in combinaton with the selected monomers of particulate, usually mineral, fillers such as finely divided silica. These various ingredients are combined in proportion and in such manner as to provide a combination of properties in both the uncured and cured state effective to render the compositions useful for dental purposes.
Polymerizable compositions for the production of formed-in-place artificial nails must satisfy a different set of conditions and hence must demonstrate a different combination of uncured and cured properties.
Artificial fingernals must adhere, not to tooth enamel but to natural nails composed essentialy of keratin, which is a protein. The adhesion characteristics must be such that the artificial nail can be readily removed at any time it is desired to do so. Whereas dental restorative compositions must remain in place for years, artificial fingernails are normally replaced or removed after a few days or weeks The environment to which an artificial nail is subject in use is markedly different from that of the mouth. Whereas dental compositions must resist the effects of water, it is desirable that artificial fingernails soften in water in a manner similar to natural nails. Artificial nails, in contrast to dental restorative compositions, are subjected to repeated flexing and shearing forces and hence should not crack or break under such normal conditions of use. Desirably, artificial nails should be translucent, though opaque nails are usable in instances where they are to be coated with fingernail polishes or enamels.
The consistency in the uncured state is of particular importance in artificial fingernail compositions. In use, such compositions are applied to a substrate which includes the natural nail and an extension thereof in the form of an appropriately shaped, sheet-like material to which the artificial nail composition does not adhere. The artificial nail composition must accordingly be of such consistency as to permit ready application without undue flowing or dripping, must be readily deformable yet shape retentive and must provide a smooth, attractive surface appearance.
Commercially available artificial fingernail compositions are composed of separately packaged liquid monomer and particulate catalyst components. The monomer component package may also include accelerators, thickeners, plasticizers, dyes and other ingredients. The catalyst component package may also include additional ingredients such as fillers, opacifiers and dyes.
Polymerization or curing occurs only upon mixture of the contents of the two packages. The polymerization time is determined by the mass rstio of the monomer and filler which results from the initial mixing. The concentration of the solid filler phase at the outset of polymerization controls the flexural strength, flexural modulus and impact resistance of the polymerized matrix. The initial concentration of the solid filler phase depends, in turn, on the initial filler/resin ratio, the solubility rate of the filler in the resin, and the time available for the filler to dissolve.
With respect to any given two-package products, the solubility rate of the filler in the resin is fixed; hence variation in initial filler/resin ratio will result in significant differences in the mechanical characteristics of the resulting artificial fingernail or cured matrix.
Two-package artificial fingernail formulations are conventionally applied by dipping a brush first in the liquid monomer component and then into the powder component, including the filler and the catalyst. With this procedure, control of the monomer/filler ratio is difficult. Polymerization times and the mechanical characteristics of the cured fingernail are subject to significant erratic variations.
The variance in filler/resin ratio invariably consequent from the conventional use of such two-package formulations also results in varying mixture consistencies.
Long practice with such two-package compositions is routinely required even for a skilled operator to establish a technique effective to provide the generally uniform mix consistency which is desirable for the smooth application of the formulation requisite to provide a satisfactory artificial fingernail. In addition, such two-package, chemically-curing systems afford only limited application time. On the average only from two to four minutes are available in which to build and shape an artificial nail before the mixture becomes unmanageable due to the onset of curing.
The consequence is an uneconomical initial waste of material and the practical limitation of the use of artificial fingernails to professional manicurists.
Presently available artificial fingernail formulations including methylmethacrylate or ethylmethacrylate monomer irritate and sensitize skin and are dermatologically unacceptable. The substitution of other monomers for methyl- or ethylmethacrylate has resulted in unsatisfactory artificial nails which lack a hard-cured surface due to oxygen inhibition of polymerization.
Attempts to replace methyl- or ethylmethacrylate have focused on acrylate or methacrylate monomers of higher molecular weight. Biologically acceptable monomers of this type, e.g., acrylic esters which include large or high molecular weight alcohol radicals yield artificial fingernals which are brittle and hence crack or break. Such artificial nails, moreover, become increasingly brittle with age. This problem is not satisfactorily solved by the use of conventional plasticizers such as dibutyl phthalate. Such plasticizers, when used in effective amounts, tend to weaken the artificial nail, impair its resistance to organic solvents, impair its adhesion to the natural nails, and in some cases to introduce new biological and dermatological problems.
These various problems which attend self-cured, two-packaged artificial fingernail compositions are largely alleviated by the single package, photopolymerizable compositions of this invention.